it’s more that Shawna is acting so animé it hurts.
“The boy/girl/esper/alien/time traveler/slider/superhero/sentient insect colony/other supernatural being I love has joined a club! I shall join too, and he/she/they(singular)/they(plural) will fall in love with me! (delete all that do not apply.)”

But quite likely in Hiroshi’s grade. There’s rather more socialising within grades than across grades, and (as you point out) it was clear that the two of them were at least somewhat acquainted and on first-name talking terms even before Hiroshi went from pupil to pupa.

We know Hiroshi is two years ahead of Castela, plus he lost a year, which would make him sixteen. That’s a pretty big mismatch at that age. Of course, when I was 17, I had a thirteen-year-old girlfriend, but she was more emotionally mature than I was. As for Timothy, he’s part wolf, so he can smell the pheromones rolling off Shawna. And the hormones, too, probably.

I doubt is will be easy for Shawna to worm her way into an “assignment” Daylla has engineered to pair Castela and Hiroshi, [if the flood od Double-Double Entendres are any indication.] That said, this is more the tingle of Anime Angst. Timothy knows something, and knows HER.